Image forming device

ABSTRACT

An image forming device ( 2 ) comprises a first connector ( 3 ) and a second connector ( 4 ) for connecting a printer engine ( 1 ) arranged therein, with a first external device ( 5 ) and a second external device ( 6 ); and a control unit ( 7 ) having an alternate operation mode in which the communications between the first external device ( 5 ) and the second external device ( 6 ) through the first connector ( 3 ) and the second connector ( 4 ) are alternately performed in a predetermined cycle. The control unit ( 7 ) enables reception of a command and/or a print starting signal from one of the first and second external devices ( 5, 6 ) during communication with the external device, and rejects reception of the command

TECHNICAL FIELD

[0001] This invention relates to an image forming device such as aprinter to which it is possible to connect an external device such as ascanner or controller. More particularly, the invention relates to animage forming device to which a plurality of external devices can beconnected so that image data from these external devices can be receivedefficiently and the images printed out.

BACKGROUND ART

[0002] In the prior art, an image forming device of this kind has asingle connector for connecting an external device (a scanner orcontroller, etc.), and a certain single external device desired by theuser can be used upon being connected to this connector.

[0003] For example, the user of such an image forming device is requiredto make an alternative selection between use of a scanner uponconnecting the same or user of a network-connected controller uponconnecting the same. If the user wises to employ several externaldevices simultaneously, the user must manually detach the externaldevice from the connector each time and re-connect the connector to thedesired external device.

[0004] A proposal that has been made in order to eliminate thisinconvenience is to allow a printer engine to be monopolized or occupiedby any of two or more external devices by having the user change over aswitch manually (see Japanese Patent Laid-Open Application No.2000-332922). Though this proposal does away with the aforementionedtroublesome operation of detaching and re-connecting a connectormanually, that fact remains that a manual switching operation isrequired. A further improvement, therefore, is needed.

[0005] Accordingly, in order to comply with the above-mentioned need, anobject of the present invention is to provide an image forming device inwhich the number of connectors for connection to external devices ismade two or more so that connection to a plurality of external devicesis made possible, wherein the image forming device is additionallyprovided with a selective changeover capability to make possiblecommunication with a plurality of external devices at any time as wellas control of each device independently.

[0006] A further object of the present invention is to simplify thestructure of the image forming device and provide the image formingdevice in a form in which signals from each of external devices will notbe lost.

DISCLOSURE OF THE INVENTION

[0007] According to the present invention, which is set forth in claim1, the foregoing objects are attained by providing an image formingapparatus characterized by having a printer engine, first and secondconnectors for connecting the printer engine to first and secondexternal devices, and a control unit having an alternate operation modein which communication with the first and second external devices isperformed alternatingly by changing over communication at apredetermined cycle, the control unit, during communication with eitherone of the first and second external devices, enabling reception ofcommands and/or a print-start signal from this external device andrefusing reception of commands and a print-start signal from the otherexternal device; and providing an interval in which reception ofcommands and a print-start signal from both external devices is refusedfor a predetermined period of time when communication is changed overfrom one external device to the other external device.

[0008] The image forming device according to the present inventioncommunicates with first and second external devices alternatingly bychanging over between these devices automatically at a predeterminedcycle, thereby making it possible to receive commands and/or aprint-start signal from an external device during communicationtherewith. By virtue of such an alternate operation mode, a single imageforming device can be used with facility by a plurality of externaldevices by allowing it to be monopolized or exclusive by the externaldevices when appropriate. Furthermore, when the above-mentionedchangeover in communication is made, an interval in which reception ofcommands and a print-start signal from both external devices is refusedfor a predetermined period of time is provided, thereby preventing lossof commands or a print-start signal (reception error), which can occurat the time of changeover.

[0009] According to the present invention set forth in claim 2, theimage forming device described in claim 1 is characterized in that whena print-start signal is received from the one external device duringcommunication therewith, a transition is made to an exclusive operationmode in which the printer engine is monopolized or occupied by thisexternal device.

[0010] Furthermore, according to the present invention set forth inclaim 3, the image forming device described in claim 2 is characterizedin that the printer engine continues to be monopolized by the oneexternal device for a predetermined period of time following the end ofprinting, the exclusive operation mode continues if a new print-startsignal is issued within this predetermined period of time, and atransition is made to the alternate operation mode if a new print signalis not issued within the predetermined period of time.

[0011] Thus, if the printer engine receives a print-start signal fromeither of the external devices during communication therewith, atransition is made to the exclusive operation mode so that the printerengine may receive image data or the like from this external device andperform printing. For a predetermined period of time following the endof such printing, the printer engine continues to be monopolized by thisexternal device and stands by for issuance of a new print-start signalfrom this external device. This is desirable in that operation is mademore nimble as when printing is performed in successive fashion.

[0012] Furthermore, according to the present invention set forth inclaim 4, the image forming device described in claim 1 is characterizedin that when a specific command is received from the one external deviceduring communication therewith, a transition is made to an exclusiveoperation mode in which the printer engine is monopolized by thisexternal device.

[0013] Furthermore, according to the present invention set forth inclaim 5, the image forming device described in claim 4 is characterizedin that the exclusive operation mode is cancelled and a transition ismade to the alternate operation mode if a print-start signal is notissued from the external device within a predetermined period of timefollowing transition to the exclusive operation mode.

[0014] In the image forming device set forth in claims 4 and 5, thetransition is made to the exclusive operation mode when the printerengine receives a specific command signal from either of the externaldevices during communication therewith. The printer engine then standsby for a predetermined period of time in order to receive a print-startsignal from this external device. If a print-start signal is not issuedwithin this predetermined period of time, the exclusive operation modebased upon this external device is cancelled and a transition is made tothe alternate operation mode in order to receive the next commandsignal.

[0015] According to the present invention set forth in claim 6, theimage forming device described in claims 1 to 5 is characterized in thatthe exclusive operation mode continues if a new print-start signal isissued within a predetermined period of time following the end ofprinting, and a transition is made to the alternate operation mode if anew print-start signal is not issued within this predetermined period oftime.

[0016] According to the present invention set forth in claim 7, theimage forming device described in claims 1 to 5 is characterized byfurther provision of selection means capable of specifying freelywhether the printer engine is monopolized or occupied by the firstexternal device or the second external device.

[0017] According to the present invention set forth in claim 8, theimage forming device described in claims 1 to 7 is characterized in thatthe first and second external devices are a scanner and a controller.

[0018] According to the present invention, which is set forth in claim9, the foregoing objects are attained by providing an image formingapparatus characterized by having a printer engine, first and secondconnectors for connecting the printer engine to first and secondexternal devices, and a control unit having an alternate operation modein which communication with the first and second external devices isperformed alternatingly by changing over communication at apredetermined cycle, the control unit issuing a busy signal indicatingwhether the printer engine is capable of receiving a command from eachexternal device and a request signal indicating whether the printerengine is capable of receiving a print-start signal from each externaldevice; notifying, while the printer engine communicates with one of theexternal devices, the other external device by the busy signal and therequest signal that a command and print-start signal cannot be receivedfrom this other external device; following notification, notifying boththe first and second external devices for a predetermined period of timethat a command and print-start signal cannot be received; then,following another predetermined period of time, communicating with theother external device and notifying the one external device by the busysignal and the request signal that a command and print-start signalcannot be received from this one external device; and repeating thisoperation at a predetermined cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a block diagram illustrating one example of an imageforming system that incorporates an image forming device according tothe present invention;

[0020]FIG. 2 is a diagram useful in describing form of signalcommunication of the image forming device according to the presentinvention;

[0021]FIG. 3 is a flowchart illustrating a state in which an externaldevice A has been selected;

[0022]FIG. 4 is a flowchart illustrating a state in which the externaldevice A has been deselected;

[0023]FIG. 5 is a flowchart illustrating a state in which an externaldevice B has been selected; and

[0024]FIG. 6 is a flowchart illustrating a state in which the externaldevice B has been deselected.

BEST MODE FOR CARRYING OUT THE INVENTION

[0025] A preferred embodiment of the present invention will now bedescribed with reference to the drawings.

[0026]FIG. 1 is a block diagram illustrating the structure of an imageforming system in which external devices, namely a scanner 5 and acontroller 6, are connected to an image forming device 2 according tothe present invention. This system includes the image forming device 2provided with a printer engine 1 for forming an image on printing paperin accordance with sent image data, a first connector 3 having aninsertion slot formed in a side wall, etc., of the image forming device2, a second connector 4 similarly having an insertion slot formed in aside wall, etc., of the image forming device 2, and a first externaldevice 5 and a second external device 6 connected to the image formingdevice 2 via the first and second connectors.

[0027] In the illustrated system, a scanner is illustrated as the firstexternal device 5 and a controller as the second external device 6,though the present invention is not limited to connection to theexternal devices mentioned. Further, in the illustrated system, anarrangement in which the two external devices, namely the scanner andthe controller, are connected to the image forming device is shown.However, the present invention is applicable even if the arrangement isone in which three or more external devices are connected.

[0028] For the sake of convenience in the description that follows, thefirst external device 5 will be described as “scanner 5” and the secondexternal device 6 will be described as “controller 6”.

[0029] The printer engine 1 is connected to the first connector 3 via aninterface switching control unit 7 within the image forming device 2,and has a function for receiving and printing out an image read by thescanner 5, which is connected to the connector 3 by a special-purposeline 8.

[0030] An image forming unit 11, which constitutes the core of theprinter engine 1, is capable of employing an image forming systemsimilar to an image forming unit used in a digital copier or digitalprinter, etc., that utilizes electrophotograpy. For example, the systemmay be a heretofore known image forming system including anelectrophotographic photosensitive drum and a charging unit, imageexposing unit, developing unit and transfer unit disposed in thevicinity of the drum. Among these, the image exposure unit is anexposure unit that is capable of responding to a digital signal andutilizes a LED or laser. This is of the type which forms anelectrostatic latent image on the photosensitive drum in accordance withimage data that has been subjected to image processing and transmittedfrom an external device.

[0031] Further, an ink-jet or thermal-transfer image forming system canbe used instead of an image forming system that utilizeselectrophotography.

[0032] In a manner similar to that described above, the printer engine 1is connected to the second connector 4 via the interface switchingcontrol unit 7, accepts image data from a computer via the controller 6connected to the connector 4 by a special-purpose line 9.

[0033] To achieve this, the controller 6 is connected to a computer 100,such as an external personal computer or printer server, by a networkline or special-purpose line.

[0034] The printer engine 1 further includes, in addition to the imageforming unit 11, an interface 12 for accepting commands, a print-startsignal and image data, etc., from an external device sent via theinterface switching control unit 7; a control unit (CPU) 13 foroutputting image data, which has been accepted through the interface 12,to the image forming unit 11; and a data read/write RAM 14 connected tothe control unit 13 and used to control the control unit 13. A suitableprinting operation is performed by such an arrangement.

[0035] The scanner 5 acting as the first external device and thecontroller 6 acting as the second external device will be describednext.

[0036] The scanner 5 connected to the first connector 3 reads an analogoriginal image optically by an image sensing device such as a CCD,thereby obtaining digital image data. In the illustrated example, thescanner has a control unit 51 for performing overall control of thescanner; an image reading unit 52 for reading the original image by aCCD or the like and converting the image to image data; a RAM 53 fortemporarily storing the read image data in order that image processingor the like may be applied; a ROM 54 storing a control program and thelike; an interface 55 for sending image data to the image forming device2; a connector 56 provided in the side wall, etc., of the scanner 5 asthe output end of the interface 55; an image processing unit 57 forapplying image processing to the image data read; and an operation panel58 for instructing (commanding) operation of and making inputs to thescanner or printer engine 1.

[0037] These means perform the above-mentioned functions and implementfunctions for operating as a scanner. In particular, the control unit51, in addition to performing control of the scanner itself, such ascommunication and processing of image data read by the image readingunit 52 and control of the operation panel 58, implements a function forcommanding the interface switching control unit 7 of the image formingdevice 2 by a command such as a print requirement or a print-startsignal in order to switch monopolization of the printer engine 1 to thescanner 5. The functions of these transmitted signals and commands willbe described in detail later.

[0038] The controller 6 connected to the second connector 4 has acontrol unit 61 for controlling the overall controller. The control unit61 accepts print data such as commands or image data via an interface 62and connector 66 through the network line or special-purpose line towhich the computer 100, etc., is connected. This print data istransmitted to the interface switching control unit 7 of the imageforming device 2 via a connector 64.

[0039] The interface switching control unit 7 outputs this data to theprinter engine 1 when conditions described later are satisfied. Itshould be noted that the print data that has been received from thecomputer 100 is stored in the RAM 65 temporarily as necessary and isoutput upon being expanded into bitmap data.

[0040] As set forth above, the control unit 61 controls communication ofsignals through a network line or special-purpose line and controlscommunication of signals with the control unit 13 of the printer engine1 via the interface switching control unit 7 within the image formingdevice 2.

[0041] Furthermore, it may be so arranged that control of an operationpanel (not shown) provided on the image forming device 2 is carried outby the control unit 61. It should be noted that communication of signalsbetween the controller 6 and interface switching control unit 7 iscarried out via an interface 63 and the connector 64, which is connectedthereto.

[0042] Though the scanner 5 and controller 6 are provided externally ofthe image forming device 2 in the illustrated example, these may bebuilt in the image forming device 2.

[0043] With reference again to the image forming device 2, the latterhas the interface switching control unit 7 for switching the printerengine 1 so that it may be monopolized or occupied by either the scanner5 or controller 6 in order to support printing based upon a signal fromthe scanner 5 and printing based upon a signal from the controller 6, asset forth earlier.

[0044] The interface switching control unit 7 has an interface 72 forcommunication of signals with the CPU 13 of printer engine 1, aninterface 74 for communication of signals with the scanner 5 via thefirst connector 3, an interface 73 for communication of signals with thecontroller 6 via the second connector 4, and a control unit 71 forperforming control so as to change over the flow of signals through eachof these interfaces 72, 73 and 74.

[0045] The control unit 71 has an alternate operation mode for switchingbetween communication with the scanner 5 and communication with thecontroller 6 alternatingly at a predetermined cycle via the firstconnector 3 and second connector 4, and an exclusive operation mode inwhich the printer engine 1 is exclusive or monopolized by the scanner 5or controller 6.

[0046] In the alternate operation mode, the control unit 71 makes itpossible to receive a command and/or a print-start signal from whicheverof the scanner 5 or controller 6 is communicating, and refuses receptionof a command or print-start signal from the other of these devices.

[0047] If the control unit 71 receives a command and/or print-startsignal from the communicating external device during communicationtherewith, the printer engine 1 is changed over to the exclusiveoperation mode, in which the printer engine is monopolized by thisdevice.

[0048] For example, with regard to the scanner 5, the printer engine 1is monopolized by the scanner 5 when the control unit 71 receives aspecific command (e.g., an exclusive command or a command for selectinga paper-feed tray, described later) from the scanner 5 duringcommunication with the scanner 5. Owing to such monopolization, theprinter engine 1 performs printing in accordance with image data fromthe scanner 5.

[0049] Following the end of printing, the printer engine 1 continues tobe monopolized or occupied by the scanner 5 for a predetermined periodof time. If a new print start command is issued from the scanner 5within this predetermined period of time, the monopolized or exclusiveoperation mode is continued and the printing operation continues to beperformed.

[0050] Conversely, if a new print-start signal is not issued from thescanner 5 within the above-mentioned period of time, a transition ismade to the alternate operation mode.

[0051] This operation is carried out periodically with respect to thescanner 5 and controller 6. When communication is switched from thescanner 5 to the controller 6 or vice versa, an interval in whichreception of commands or print-start signals from both of these devicesis refused for a predetermined period of time is provided. As a result,a situation is which a signal from either of these devices is lost isprevented.

[0052] In addition to the above components, specific selection means 75is provided and connected to the control unit 71. The specific selectionmeans 75 enables the user to forcibly specify which of the externaldevices is to monopolize the printer engine 1 by operating a switch orthe like on an operation panel.

[0053] The role of the above-mentioned commands and print-start signalwill now be described in line with an embodiment.

[0054]FIG. 2 illustrates an example of signals transmitted between theimage forming device 2 and an external device (scanner 5, controller 6).The individual signals are as described below. Though FIG. 2 illustratesonly the signals communicated with one of the external devices, namelythe scanner 5, similar signals are also communicated with the otherexternal device, namely the controller 6. An embodiment will bedescribed below with the two external devices being referred to asexternal device A and external device B.

[0055] POWER: This is a signal which indicates that the power supply ofthe interfaces of the image forming device have been turned on.

[0056] READY: This is a signal which indicates that the printer engine 1is in the ready state.

[0057] REQUEST: This is a signal which reports that a print-start signal“PRINT” from the external device is capable of being received by theprinter engine 1.

[0058] COMMAND: This is a signal which specifies the substance of datainput to the printer engine 1.

[0059] STATUS: This is a signal which specifies input/output of the databus.

[0060] PRINT: This is a print-start signal from the external device.

[0061] SYNCHRO: This is a horizontal synchronizing signal whichindicates the start of horizontal scanning.

[0062] BUSY: This is a signal which indicates that a “STROBE” signalcannot be received.

[0063] STROBE: This is a signal which indicates that data on the bus isvalid.

[0064] IP CUT: The printing paper is a paper roll. This signal is forcutting the paper roll.

[0065] DATA BUS: This is a bi-directional data bus.

[0066] Command and image data is input to the printer engine 1 by thissignal line.

[0067] <Overview of Communication Control>

[0068] Thus, the image forming device 2 uses a plurality of signals inorder to communicate with the external devices A, B. As mentioned above,these signals include the “busy signal (BUSY)” which indicates whetherthe printer engine 1 is capable of receiving a command from the externaldevices A, B for selecting a specific paper-feed tray, etc. The rule issuch that when the “busy signal” is “H”, the applicable external devicecannot transmit the command to the printer engine 1.

[0069] Similarly, the rule is such that when the “request signal(REQUEST)” which indicates whether the printer engine 1 is capable ofreceiving the print-start signal from the external devices A, B is “H”,the applicable external device cannot transmit the print-start signal(PRINT) to the printer engine 1.

[0070] In a case where the printer engine 1 communicates with the oneexternal device A at the time of standby (standby state), during thistime the printer engine 1 holds the “busy signal” at “H” with respect tothe external device B to notify that a command from the external deviceB cannot be received. At the same time, the printer engine 1 holds the“request signal (REQUEST)” at “H” with respect to the external device Bto notify that the print-start signal from the external device B cannotbe received.

[0071] For the sake of convenience, this state shall be referred to as“external device A selected”, “external device B deselected” below.

[0072] When communication with the external device A ends, the printerengine 1 holds the “busy signal” and “request signal” at “H” withrespect to the external device A for a fixed period of time (e.g., 500ms) to give notification of the fact that commands and a print-startsignal from the external device A cannot be received. At this time theprinter engine 1 continues to hold the “busy signal” at “H” also withrespect to the external device B, thereby preventing loss of receptionof commands or the like, which can occur when switching between theexternal device A and the external device B. The length of time forpreventing this loss of signals may be 1 ms, by way of example.

[0073] Next, the “busy signal” of logic “H” being sent to the externaldevice B is made “L” to notify of the fact that communication with theexternal device B is possible. At the same time, the “request signal” oflogic “H” being sent to the external device B is made “L” to notify ofthe fact that the print-start signal from the external device B iscapable of being received.

[0074] By thenceforth following a similar procedure, communication withthe external devices A and B is changed over repeatedly at apredetermined cycle. (This is the alternate operation mode.)

[0075] <Overview of Printing Control>

[0076] When the print-start signal is issued from the selected externaldevice A or B, as mentioned above, the printer engine 1 responds bycompleting printing and, until a fixed period of time (30 s) elapses,the interface switching control unit 7 selects the applicable channeland holds the other channel deselected. (This is the monopolized orexclusive operation mode.)

[0077] Further, if a command for selecting a specific paper-feed tray isreceived by the printer engine 1, which has a plurality of paper-feedtrays, then, in response, the printer engine 1 is placed in themonopolized or exclusive operation mode, in which the applicable channelis selected and the other channel deselected, for the fixed period oftime (30 s).

[0078] If the applicable external device issues the print-start signalwithin this interval, the aforesaid “exclusive operation mode” continuesif the print-start signal is not issued within this interval, however, atransition is made to the “alternate operation mode”.

[0079] <Printer-Engine Forcible Exclusive Command>

[0080] When the print-start signal or a command such as for selection ofthe paper-feed tray is received, a state is attained in which theprinter engine 1 is monopolized by the applicable external device, asset forth above. However, there is separately provided a command(exclusive command) by which the printer engine 1 is explicitly (i.e.,forcibly) dedicated solely to either of the external devices. Uponreceiving this exclusive command, a state is attained in which theprinter engine 1 is monopolized or occupied by the applicable externaldevice; there is no transition to the alternate operation mode.

[0081] However, in a case where an exclusive-cancel command is received,and in a case where no command is received over a fixed period of time(e.g., 3 min) following reception of the exclusive command, theexclusive operation mode is cancelled and a transition is made to thealternate operation mode.

[0082] Next, the flow of processing according to a preferred embodimentof the present invention will be described with reference to FIGS. 3 to6.

[0083] The external device A and the external device B are placed in thedeselected state (step 1). The external device A is selected (step 2)and it is determined whether a command is being received from theexternal device A (step 3). If a command is being received from theexternal device A, processing for responding to the external device A isexecuted (step 4).

[0084] If a command from the external device A is not being received, onthe other hand, it is determined whether print start is being receivedfrom the external device A (step 6).

[0085] If print start is being received from the external device A, thenthe exclusive mode is established and printing is executed (step 7).Furthermore, control returns to step 3.

[0086] On the other hand, in a case where print start is not beingreceived from the external device A, and after processing for respondingto the external device A has been executed at step 4, it is determinedwhether a fixed period of time has elapsed since selection of theexternal device A (step 5). Control returns to step 3 if the fixedperiod of time has not elapsed. In a case where the fixed period of timehas elapsed, it is determined whether operation in the exclusive mode isin progress (step 8).

[0087] If operation in the exclusive mode is in progress, then it isdetermined whether a fixed period of time has elapsed since the end ofprinting (step 9). If the fixed period of time has elapsed, then theexclusive mode is cancelled (step 10). If the fixed time has notelapsed, control returns to step 3.

[0088] In a case where operation in the exclusive mode is not inprogress at step 8, and after the exclusive mode is cancelled at step10, the external device A is deselected (step 11). It is determinedwhether a fixed period of time has elapsed since deselection of theexternal device A (step 12).

[0089] If the fixed period of time has not elapsed since deselection ofthe external device A, then it is determined whether a command from theexternal device A is being received (step 13). If the command is beingreceived, the external device A is selected and processing forresponding to the external device A is executed (step 14). Furthermore,control returns to step 11.

[0090] On the other hand, if a command from the external device A is notbeing received, then it is determined whether print start is beingreceived from the external device A (step 15).

[0091] If print start is being received from the external device A thenthe exclusive mode is established and printing is executed (step 16).Furthermore, control returns to step 3. If the fixed period of time haselapsed at step 12 following deselection of the external device A, thenexternal device B is selected (step 17).

[0092] It is determined whether a command from the external device B isbeing received (step 18). If a command from the external device B isbeing received, processing for responding to the external device B isexecuted (step 19).

[0093] On the other hand, if a command from the external device B is notbeing received, then it is determined whether print start from theexternal device B is being received (step 20).

[0094] If print start is being received from the external device B, theexclusive mode is established and printing is executed (step 21).Furthermore, control returns to step 18.

[0095] On the other hand, in a case where print start is being receivedfrom the external device B at step 20 and after processing forresponding to the external device B has been executed at step 19, it isdetermined whether a fixed period of time has elapsed since selection ofthe external device B (step 22). If the fixed period of time has notelapsed, control returns to step 18. If the fixed period of time haselapsed, then it is determined whether operation is in progress in theexclusive mode (step 23).

[0096] If operation in the exclusive mode is in progress, then it isdetermined whether a fixed period of time has elapsed since the end ofprinting (step 24). If the fixed period of time has elapsed, then theexclusive mode is cancelled (step 25). If the fixed time has notelapsed, control returns to step 18.

[0097] In a case where operation in the exclusive mode is not inprogress at step 23, and after the exclusive mode is cancelled at step25, the external device B is deselected (step 26). It is determinedwhether a fixed period of time has elapsed since deselection of theexternal device B (step 27).

[0098] If the fixed period of time has not elapsed since deselection ofthe external device B, then it is determined whether a command from theexternal device B is being received (step 28). If the command is beingreceived, the external device B is selected and processing forresponding to the external device B is executed (step 29). Furthermore,control returns to step 26.

[0099] On the other hand, if a command from the external device B is notbeing received, then it is determined whether print start is beingreceived from the external device B (step 30). If print start is beingreceived from the external device B then the exclusive mode isestablished and printing is executed (step 31). Furthermore, controlreturns to step 18.

[0100] If print start is not being received from the external device B,then control returns to step 27. If the fixed period of time has elapsedat step 12 following deselection of the external device B, then controlreturns to step 2.

INDUSTRIAL APPLICABILITY

[0101] Thus, in the image forming device according to the presentinvention, a plurality of external devices can be connected in parallel.In addition, a complicated operation such as changing over of a switchrequired in the prior art is made unnecessary, and it is possible toperform printing based upon image data from a prescribed external deviceas appropriate.

[0102] Further, a predetermined OFF period (a period in which receptionof a command or print-start signal is refused from any external device)is provided at intervals where the plurality of external devices areswitched among, thereby making it possible to prevent missed receptionof commands or the like, which can occur at the time switching.

[0103] Further, since a function through which it is possible to specifyan external device which freely (forcibly) monopolizes the image formingdevice is provided, one of the parallel-connected external devices canbe selected and allowed to monopolize the image forming device in linewith the wishes of the user as in the manner of the prior art.

What is claimed is:
 1. An image forming apparatus characterized byhaving a printer engine, first and second connectors for connecting saidprinter engine to first and second external devices, and a control unithaving an alternate operation mode in which communication with saidfirst and second external devices is performed alternatingly by changingover communication at a predetermined cycle, said control unit, duringcommunication with either one of said first and second external devices,enabling reception of commands and/or a print-start signal from thisexternal device and refusing reception of commands and a print-startsignal from the other external device; and providing an interval inwhich reception of commands and a print-start signal from both externaldevices is refused for a predetermined period of time when communicationis changed over from one external device to the other external device.2. An image forming device according to claim 1, characterized in thatif a print-start signal is received from said one external device duringcommunication therewith, a transition is made to an exclusive operationmode in which the printer engine is monopolized by this external device.3. An image forming device according to claim 1, characterized in thatthe printer engine continues to be monopolized by said one externaldevice for a predetermined period of time following the end of printing,the exclusive operation mode continues if a new print-start signal isissued within this predetermined period of time, and a transition ismade to the alternate operation mode if a new print signal is not issuedwithin the predetermined period of time.
 4. An image forming deviceaccording to claim 1, characterized in that when a specific command isreceived from said one external device during communication therewith, atransition is made to an exclusive operation mode in which said printerengine is monopolized by this external device.
 5. An image formingdevice according to claim 4, characterized in that said exclusiveoperation mode is cancelled and a transition is made to said alternateoperation mode if a print-start signal is not issued from said externaldevice within a predetermined period of time following transition tosaid exclusive operation mode.
 6. An image forming device according toclaim 5, characterized in that the exclusive operation mode continues ifa new print-start signal is issued within a predetermined period of timefollowing the end of printing, and a transition is made to the alternateoperation mode if a new print-start signal is not issued within thispredetermined period of time.
 7. An image forming device according toany one of claims 1 to 6, characterized by further having selectionmeans capable of specifying freely whether the printer engine ismonopolized by said first external device or second external device. 8.An image forming device according to any one of claims 1 to 7,characterized in that said first and second external devices are ascanner and a controller.
 9. An image forming apparatus characterized byhaving a printer engine, first and second connectors for connecting saidprinter engine to first and second external devices, and a control unithaving an alternate operation mode in which communication with saidfirst and second external devices is performed alternatingly by changingover communication at a predetermined cycle, said control unit issuing abusy signal indicating whether the printer engine is capable ofreceiving a command from each external device and a request signalindicating whether the printer engine is capable of receiving aprint-start signal from each external device; notifying, while theprinter engine communicates with one of the external devices, the otherexternal device by the busy signal and the request signal that a commandand print-start signal cannot be received from this other externaldevice; following notification, notifying both the first and secondexternal devices for a predetermined period of time that a command andprint-start signal cannot be received; then, following anotherpredetermined period of time, communicating with said other externaldevice and notifying said one external device by the busy signal and therequest signal that a command and print-start signal cannot be receivedfrom this one external device; and repeating this operation at apredetermined cycle.